1. Field of the Invention
The invention relates to a magnetoresistance effects film to be used for a magnetoresistance effects element for reading out a magnetic field intensity as a signal from magnetic substances such as a magnetic record medium, and more particularly to such a magnetoresistance effects film which exhibits large change in resistance even when a small external magnetic field is applied thereto.
2. Description of the Related Art
Recently, there has been developed the improvement of sensitivity of a magnetic sensor and the densification in magnetic recording, and following such development, there has been also developed a magnetoresistance effects type magnetic sensor (hereinafter, referred to simply as a MR sensor) and a magnetoresistance effects type magnetic head (hereinafter, referred to simply as a MR head). Both of a MR sensor and a MR head read out external magnetic field signals in accordance with changes in a resistance of a reading sensor composed of magnetic material. Both of a MR sensor and a MR head have a characteristic that a relative speed to a magnetically recording medium is not dependent on regenerated outputs. Hence, there can be obtained merits that a MR sensor provides a high sensitivity, and a MR head provides a high output even in high density magnetic recording.
Japanese Unexamined Patent Publication No. 5-347013 laid open to public on Dec. 27, 1993 has suggested a magnetically recording and regenerating apparatus comprising a recording medium for magnetically storing signals therein, and a magnetoresistance effects element comprising a deposited structure composed of a substrate, an antiferromagnetic film, a ferromagnetic film, a nonmagnetic film, a soft magnetic film, a nonmagnetic film, a ferromagnetic film and an antiferromagnetic film, each of which is deposited in a driving direction relative to the recording medium. According to the Publication, there can be obtained a magnetically recording and regenerating apparatus having a high record density and further obtained a magnetoresistance effects element providing high sensitivity and regenerated output.
There has been reported another magnetoresistance effects film in Physical Review B, Vol. 43, No. 1, Jan. 1, 1991, pp 1297-1300, published by The American Physical Society. This magnetoresistance effects film has a structure comprising at least two thin soft magnetic layers separated by a thin nonmagnetic interlayer disposed therebetween. Adjacent to one of the thin soft magnetic layers is disposed a thin antiferromagnetic film to provide an anti-magnetic force thereto to thereby cause rotation of the magnetization with an external magnetic field which is different from that of the other of the thin soft magnetic layers disposed adjacent to the one of the thin soft magnetic layers via the non-magnetic interlayer. Thus, a change in resistance is caused.
Japanese Unexamined Patent Publication No. 4-358310 laid open to public on Dec. 11, 1992, which is based on U.S. patent application Ser. No. 625343 filed on Dec. 11, 1990, has also suggested a similar magnetoresistance effects film. The Publication has disclosed a magnetoresistance sensor utilizing spin-valve effect.
The above mentioned report has suggested, as a practical MR head, a magnetoresistance effect element having a structure comprising a soft magnetic layer, a non-magnetic insulator, a multilayered structure, a non-magnetic insulator and a soft magnetic layer successively deposited in this order.
Though the magnetoresistance effects films suggested in the above identified report and Publication can operate even with a small external magnetic field, it is necessary for them to apply a signal field thereto in a direction of an axis of easy magnetization when it is intended to use the magnetoresistance effects films as a practical MR sensor or MR head. When they are to be used as a magnetic sensor, there has been posed problems that they do not exhibit a change in resistance when a magnetic field has an intensity of approximately zero, and that there would be found nonlinearity such as Barkhausen jump caused due to discontinuous displacement of domain walls.
In addition, it is necessary to use FeMn having inferior corrosion resistance as material of which an antiferromagnetic film is composed. Furthermore, there are another problems that additives have to be added to the antiferromagnetic films in practical use, and a protection film has to be deposited for protecting the magnetoresistance effects films.
On the other hand, if a thin antiferromagnetic film composed of oxide or a thin permanent magnet film both of which has superior corrosion resistance is used as a magnetic film for pinging to a ferromagnetic layer, there arises a problem that a sandwiched film which is to be deposited on the oxide antiferromagnetic film or permanent magnet film and which comprises magnetic layer/nonmagnetic layer/magnetic layer would have poor crystallization, and thus the hysteresis in output is likely to appear.